1. Field of Invention
The present invention relates to a semiconductor device provided with an element which has a layer containing an organic compound over a flexible substrate, and also relates to a manufacturing method of the semiconductor device.
2. Description of the Related Art
It has been required to manufacture semiconductor devices at low cost, and development has been extensively carried out in recent years on elements such as transistors, memories, and solar cells which use layers containing organic compounds for control circuits, storage circuits, or the like (see, for example, Reference 1: Japanese Patent Laid-Open No. 2004-47791).
Various applications of semiconductor devices having the elements such as transistors, memories, and solar cells which use the layers containing organic compounds are expected, and using flexible plastic films is attempted in pursuit of reduction in size and weight.
Since plastic films have low heat resistance, it is necessary to decrease the highest temperature in a process. Therefore, the semiconductor devices using plastic films are manufactured by an evaporation method or a sputtering method using a metal mask.
Since plastic films have low heat resistance, transistors formed over plastic films cannot have as favorable electrical characteristics as transistors formed over glass substrates at present.
Consequently, such a technique is suggested that minute elements formed over a glass substrate by a photolithography step are separated from the substrate and pasted to another base material such as a plastic film (see Reference 2: Japanese Patent Laid-Open No. 2003-174153).
However, in the case of manufacturing a semiconductor device by an evaporating method or a sputtering method using a metal mask, a step of aligning the metal mask is necessary. Therefore, a problem in aligning the metal mask leads to low yield.
Moreover, in the case of manufacturing a semiconductor device by an evaporation method or a sputtering method using a metal mask, an element is designed in consideration of the misalignment. Thus, it is difficult to manufacture transistors, memories, and solar cells having minute structures, and reduction in size and weight and improvement in performance of semiconductor devices are difficult.
Moreover, in the case of separating an element which has a layer containing an organic compound, by using a separation step shown in Reference 2; specifically, in the case of forming a separation layer 102 over a substrate 101, forming an inorganic insulating layer 103 over the separation layer 102, forming a first electrode layer 104 over the inorganic insulating layer 103, forming a layer 105 containing an organic compound over the first electrode layer 104, forming a second electrode layer 106 over the layer 105 containing an organic compound, and separating an element 151 which has the layer 105 containing an organic compound and a layer 157 having the element 151 as shown in FIG. 21, there is a problem in that the separation occurs between the layer 105 containing an organic compound and the second electrode layer 106.
This is because adhesion between the layer 105 containing an organic compound and the second electrode layer 106 is low. Specifically, since the layer 105 containing an organic compound functions as an organic semiconductor, the layer 105 is formed with a material having a carrier-transporting property. The material having a carrier-transporting property does not have in general a polar substituent such as an imide group, a cyano group, or a hydroxyl group. Accordingly, the adhesion between the layer 105 containing an organic compound and the second electrode layer 106 is so low that separation occurs between the layer 105 containing an organic compound and the second electrode layer 106 in a separation step.
As a result, it is difficult to manufacture, with high yield, a semiconductor device where the element which has the layer containing an organic compound is provided over a plastic film.